At elevated temperatures and in dilute solution, we have observed lamellar surface ordering at the air-water interface of dihexadecyl dimethylammonium bromide, DHDAB, in the presence of electrolyte. With increasing temperature, the onset in ordering is observed between 35 and 40°C. At 40°C, there is an abrupt change in the lamellar spacing, from ∼33 to ∼40 Å. Furthermore, in the presence of the cosurfactant benzyl alcohol, the ordering occurs at a lower temperature, between 20 and 25°C. The change in lamellar spacing with temperature is attributed to a surface-induced transition, similar to the Lβ to Lα phase transition observed in bulk lamellar dispersions.
